Topic 8 Flashcards
How do our eyes respond to bright light?
Stimulus: Bright light Receptors: Photoreceptors in the eye Passed along sensory neurone Processed by CNS Passed along motor neurone Effectors: Circular muscles in iris Response: Circular muscles contract to constrict pupils
Which iris muscles contract to narrow the pupil?
Circular
Which iris muscles contract to dilate pupil?
Radial
How do our eyes respond to dim light?
Stimulus: Dim light Receptors: Photoreceptors in the eye Passed along sensory neurone Processed by CNS Passed along motor neurone Effectors: Radial muscles in iris Response: Radial muscles contract to widen the pupils
What is the hormonal system made up of?
Glands and hormones
What are glands?
A group of cells specialised to secretes a useful substance
What is a hormone?
Chemical messengers. Often proteins, peptides and steroids
What is a target cell?
A cell with a specific receptor for a hormone
Characteristics of nervous communication?
Electrical impulses
Faster response
Localised response
Short-lived response
Characteristics of hormonal communication?
Uses chemicals
Slower response
Widespread response
Long-lived response
What is the fovea?
Area of the eye with lots of photoreceptors
How are nerve impulses carried between the eye and brain?
The optic nerve - a bundle of neurones
How do photoreceptors work?
Light absorbed by light-sensitive pigments which are bleached, causing a chemical change. This triggers a nerve impulse along a bipolar neurone
What is the role of a bipolar neurone?
Connects photoreceptors to the optic nerve
What are the two types of photoreceptor in the human eye?
Rods and cones
What is the light sensitive pigment in rods?
Rhodopsin
What is rhodopsin made of?
Retinal and opsin
What happens when a rod is not stimulated?
1) Sodium ions pumped out of rod cell by active transport
2) Sodium ions diffuse back in through open sodium channels
3) Inside of cell is only slightly negative compared to outside - said to be depolarised
4) Triggers the release of neurotransmitters
5) Neurotransmitters inhibit the bipolar neurone so no action potential is fired
What happens when a rod is stimulated?
1) Light energy breaks rhodopsin down into retinal and opsin - this is bleaching
2) Bleaching causes sodium channels to close
3) Sodium ions pumped out but don’t diffuse in
4) Sodium ions build up on outside, making the inside much more negative - hyperpolarisation
5) Hyperpolarisation stop release of neurotransmitter
6) Bipolar neurone not inhibited so depolarises. Possible to send action potential to brain
What do all neurones share?
A cell body with a nucleus, plus normal cell contents. Cell body has extensions that connect to other neurones
What are dendrites?
Extensions that carry impulses toward the cell body
What are axons?
Extensions that carry impulses away from the cell body
What is the structure of a motor neurone?
Many short dendrites carry impulses from CNS to cell body
One long axon carries nerve impulses to effector cells
What is the structure of a sensory neurone?
One long dendrite carries nerve impulses from receptor cells to the cell body
One short axon carries nerve impulses from the cell body to the CNS
What is the structure of relay neurones?
Many short dendrites
Many short axons
What are the three types of neurone?
Motor, sensory and relay
What is the function of a relay neurone?
Transmit action potentials through the CNS
What is the state of a neurone membrane at rest?
Polarised - outside more positive than the inside
What is the difference in voltage across the neurone membrane at rest called?
Resting potential
What is the resting potential of neurone membrane?
Around -70mV
What features of the cell membrane allow the resting potential to be maintained?
Sodium-potassium pumps and potassium ion channels
What do sodium-potassium pumps do?
Use active transport to move three sodium ions out of the neurone for every two potassium ions moved in
What do potassium ion channels do?
Allow facilitated diffusion of potassium ions out of the neurone, down their concentration gradient
How is resting potential maintained?
Na+ ions pumped out and the membrane is impermeable to them so they cannot re-enter. Creates concentration gradient. K+ ions pumped in but can diffuse back out. Makes outside of cell more positively charged
What happens to neurone membranes when they are stimulated?
They become depolarised. Sodium ion channels open so the membrane becomes more permeable to sodium. Sodium ions diffuse into the neurone down the concentration gradient. Inside of the neurone becomes less negative
How does an action potential proceed?
Stimulus Depolarisation Repolarisation Hyperpolarisation Resting potential
What happen during depolarisation?
If the potential difference reaches the threshold of around -55mV more sodium ion channels open and sodium ions diffuse into the neurone
What happens during repolarisation?
At a PD of around +30mV the sodium ions close and potassium ion channels open. More potassium ions diffuse out. Membrane begins to return to resting potential.
What happens during hyperpolarisation?
Potassium ion channels are slow to close so too many potassium ions diffuse out. Potential difference becomes more negative than resting potential
What happens during the refractory period?
Ion channels are reset. Sodium-potassium pump returns membrane to its resting potential. Neurone cannot be stimulated during this period.
How does an action potential move along a neurone?
As a wave of depolarisation. Some sodium ions diffuse sideways when entering the cell. This causes sodium ion channels in the next region to open. The wave moves along because the refractory period prevents it firing backward
What does the refractory period ensure?
Action potentials don’t overlap so pass along as discrete impulses. Also ensure they are unidirectional.
What does a bigger stimulus to a neurone cause?
More frequent impulses
What can make action potentials go faster?
Myelinated neurones
What does myelinated mean?
Neurones with a myelin sheath. This is an electrical insulator.
What is a myelin sheath made of?
Schwann cell
What are the tiny patches between Schwann cells called?
Nodes of Ranvier
What happens in a myelinated neurone?
Depolarisation only happens at nodes of Ranvier where sodium ions can get through the membrane. The neurone cytoplasm conducts enough electrical charge to depolarise the next node
What is the name for the conduction in myelinated neurones?
Saltatory conduction
What is a synapse?
The junction between two neurones or a neurone and an effector cell
What is the gap in a synapse called?
The synaptic cleft
Where is the synaptic knob found?
The presynaptic neurone
What happens at the synapse?
Action potential causes voltage gated calcium ion channels to open and therefore calcium influx. This causes neurotransmitter release. Diffuse to postsynaptic membrane and bind to specific receptors. Neurotransmitters removed by reuptake or broken down by enzymes
What happens when neurotransmitters bind to receptors?
Sodium ion channels open, influx of sodium ions, causes depolarisation. May cause action potential, muscle contraction or secretion of hormone
What do synapses allow for?
Dispersion or amplification of signals. Summation of neurotransmitters from multiple neurones or repeat stimulation in a short time can mean small signals eventually add up to the threshold level.
What responses can plants have to stimuli?
Growth in response (tropism) to light (phototropism), gravity (geotropism)
How are plant responses brought about?
Growth factors - chemicals that speed up or slow down plant growth.
Where are growth factors produced?
Growing parts of the plant such as shoot tips and leave, then move to where they are needed in the plant
What do auxins do?
Difference in concentration cause difference in growth
How do plants detect light?
Photoreceptors called phytochromes
Where are phytochromes found?
Many parts of the plant including the leaves, seeds, roots and stem
What states do phytochromes exist in?
Pr and Pfr
What happens to phytochromes in darkness?
Pfr slowly converts to Pr
What happens to phytochromes in daylight?
Daylight contains more red than far-red so more Pr converted than Pfr
What four brain regions do you need to know?
Cerebrum
Hypothalamus
Medulla
Cerebellum
What is the location and structure of the cerebrum?
Largest part of brain, two halves. Top of brain. Thin outer layer called the cerebral cortex, large, highly folded surface area.
What is the function of the cerebrum?
Vision, learning, thinking, emotion
What is the location of the hypothalamus?
Found just below middle part of brain.
What is the function of the hypothalamus?
Maintains body temperature, produces hormones that control the pituitary gland
What is the location of the medulla?
At the base of the brain, top of the spinal cord
What is the function of the medulla?
Controls breathing and heart rate
What is the location of the cerebellum?
Underneath cerebrum at the back
What is the function of the cerebellum?
Coordinating movement and balance
How does a CT scan work?
Takes lots of cross sectional x-ray images of the brain. Denser structures absorb more so are lighter
What are the uses of scanners in brain visualisation?
Investigating structure, function and medical diagnosis
What is the use of CT in investigating brain structure?
Shows the major structures of the brain
What is the use of a CT or MRI in investigating brain function?
Doesn’t show function. However, if it shows damage and some patient function has been lost, the function of that part of the brain can be deduced.
What is the use of CT in medical diagnosis?
Show damaged or diseased areas. E.g blood has different density to tissue so shows up lighter - can locate damaged blood vessels
How does MRI work?
Use a strong magnetic field and radio waves to produce cross sectional images
What is the use of MRI and fMRI in investigating brain structure?
Much more detailed view of damaged or diseased tissue than CT
What is the use of MRI in medical diagnosis?
Shows damaged and diseased tissue. Eg. tumour cells respond differently to a magnetic field than normal cells so show up lighter.
How does an fMRI scan work?
More oxygenated blood flows to active areas of the brain. Molecules in oxygenated blood respond differently to a magnetic field than those in deoxygenated blood. More active areas can be identified.
What is the use of fMRI in investigating brain function?
Function carried out while in scanner causes greater brain activity in region, showing up due to blood.
What is the use of fMRI in medical diagnosis?
Show damaged and diseased regions. Allow study of conditions caused by abnormal activity in brain. E.g. fMRI taken before and during seizure can be used to locate problem area.
What five methods are used to investigate brain development?
Animal experiments, newborn studies, twin studies, brain damage studies, cross-cultural studies
Explain animal experiments with regards to investigating brain development
Study the effect of different environments on brain development of animals of the same species. Differences more likely due to nurture. Alternatively study nature by genetically modifying mice to lack a particular gene.
Explain newborn studies with regards to investigating brain development
Brain of a newborn not really affected by environment. Study what functions are there at birth and how developed different parts of the brain are.
Explain twin studies with regards to investigating brain development
Identical twins are genetically identical. Differences in brain development of separated identical twins are due to nurture. Any difference in brain development between identical and non-identical twins is likely due to nature
Explain brain damage studies with regards to investigating brain development
Development of chosen function compared between children with and without brain damage. If the function still develops, more likely due to nurture. If it doesn’t, more likely due to nature.
Explain cross-cultural studies with regards to investigating brain development
Children raised in different cultures have different environments. Large groups of children compared. Major difference more likely due to nurture
What is habituation?
Reduced response to an unimportant stimulus after repeated exposure over time
What is the visual cortex?
Part of the brain in the cerebral cortex. Receives and processes visual information. Arranged in columns of equal size for left and right eyes
How were experiments on development of the visual cortex done?
- Stitch one eye shut in a kitten
- Eye unstitched after several months
- Stitched up eye was blind
- Ocular columns larger for other eye
- Same thing done in adult cats - vision fully recovered and columns unchanged
What is the critical window?
Time period in early life that visual stimulation is necessary for normal vision to develop
What is Parkinson’s Disease?
A brain disorder than affects motor skills - neurones in part of brain controlling movement are destroyed
What neurotransmitter is involved in Parkinson’s?
Lack of dopamine - decrease in transmission of nerve impulses involved in movement
Symptoms of Parkinson’s?
Tremors and slow movement
How is Parkinson’s treated?
Drugs to increase level of dopamine in the brain
What neurotransmitter is linked to depression?
Serotonin
What does serotonin do?
Transmits nerve impulses across synapses in the parts of the brain that control mood
How is depression treated?
Drugs that increase the level of serotonin in the brain
What is L-dopa and how does it work?
- Treats Parkinson’s
- Structure very similar to dopamine
- Enters brain and is converted by an enzyme to dopamine
- Increases level of dopamine in brain
- More nerve impulses in movement area of brain transmitted
What is MDMA and what does it do?
- Ecstasy
- Inhibits reuptake of serotonin and triggers release of serotonin from presynaptic neurone
- Nerve impulses constantly triggered in parts of brain controlling mood
What use is the human genome project?
Create new drugs that target the identified proteins. E.g. inhibit an enzyme responsible for the spread of cancer cells around the body. Also shows genetic predisposition to effectiveness of certain drugs.
How are microorganisms genetically modified to produce drugs?
- Restriction enzymes isolate gene
- Gene copied using PCR
- Copies inserted into plasmids
- Plasmids transferred into microorganisms
- Microorganisms grown in large containers so they divide and produce lots of useful protein
- Protein purified and used as a drug
How are plants genetically modified to produce drugs?
- Gene inserted into bacterium
- Bacterium infects plant cell
- Gene inserted into plant cell DNA by bacterium
- Plant cell grown into adult plant
- Protein purified from plant tissues
How are animals genetically modified to produce drugs?
- Gene injected into the nucleus of a fertilised animal egg cell
- Egg cell implanted into adult animal
- Protein purified from milk of the animal
Benefits of use of GMOs?
- Agriculture crops give higher yields and more nutritious
- Pest resistant - fewer pesticides - cheaper and less environmental issues
- Cheap production of enzymes
- Human proteins produced instead of using animal proteins to treat disorders
- Vaccines produced in plant tissues don’t need refrigeration
- Reproduced using conventional farming methods
Risks of using GMOs?
- Concern about transmission of genetic material - superweeds from inbreeding of herbicide-resistant crops and wild plants
- Unforeseen consequences
- Some think it’s morally wrong to modify animals for human benefit
